In internal combustion engines, lubricating oil degrades and becomes contaminated during engine use, necessitating procedures for changing that the oil. Such oil changes account for a significant amount of "down time" over the life of an engine. It is desirable to minimize the amount of service required for internal combustion engines to thereby minimize the interruption in use of the vehicle/equipment.
It is further desirable to minimize oil changes in order to reduce the amount of used lubricating oil that is removed from engines. Waste oil must be disposed of and/or processed in order to help prevent potential environmental hazards. Such oil disposal or processing resulting in undesirable costs. Therefore, extending oil drain intervals and reducing waste disposal are of great value to vehicle/equipment operators.
Oil drain intervals for engines are conventionally set assuming the most severe operating conditions and the lowest quality of oils known to the equipment producer. As a result, the drain interval is usually highly conservative, and much shorter than necessary. Most used oil is still quite functional. In general, a practice of prematurely replacing engine oil results in: the introduction of more waste oil into the environment; increased oil consumption and import demands; and higher overall engine maintenance costs. All of these matters can be improved if the engine oil in individual vehicles is optimally utilized before being replaced.
A modern trend is toward a tiered oil drain recommendation, whereby oil change intervals are recommended based upon various levels of severity of operation. However, it is impossible for engine/equipment/vehicle manufacturers to anticipate all user operations and list different oil drain intervals for each of them. Particularly most equipment/vehicles are used in more than one kind of operation. Additionally, a complex list of oil change guidelines can be confusing to a customer.
Another known approach is to determine oil drain interval based on used oil analysis to determine whether the oil still favorably meets certain criteria. Such an analysis is performed upon a small oil sample that is manually removed from an engine crankcase. Oil replacement is postponed if the used oil analysis yields positive results. This practice has various drawbacks. Firstly, significant costs are incurred in collecting and analyzing oil samples. Secondly, used oil samples themselves become hazardous waste along with many chemicals and solvents needed to do the analysis. Thirdly, sample mix-up and labeling errors are possible, leading to erroneous conclusions. Furthermore, used oil analyses typically results in an estimated change interval based upon previous engine operation, failing to account for possible future changes in operating conditions.
Some oil change indicator systems on engines are known. However, previous engine oil indicator systems have suffered from accuracy and reliability problems in addition to other problems and therefore have not been widely implemented on engines. One attempt of an oil change indicator system is set forth in Schricker, U.S. Pat. No. 5,750,887. Schricker asserts to provide a method for determining a remaining life of oil that includes the steps of measuring a plurality of engine parameters, determining an estimate of the characteristics or properties of the engine oil as a function of the engine parameters, and trending the estimate to determine the remaining life of the engine oil. The estimated properties for engine oil include a soot estimate, a viscosity estimate, oxidation estimate, and a total base number estimate, but it is not clear how all these estimates are obtained. The method asserted by Schricker also suffers from several drawbacks. In particular, a large memory capacity would appear necessary to keep all the data necessary for trending the data and a higher computational power would appear necessary to carry out statistical trending. These have cost and practicality disadvantages. Schricker also suffers from reliability problems. For example, if an operator suddenly changes from a long period of mild engine operation suddenly to a severe engine operation, delays in the oil change warning will result because the severe operation is smoothed out by the long period of mild conditions in the past.